Field of the Invention
Embodiments of the invention relate to a geodetic surveying method for referencing a coordinate system, a geodetic surveying device and a computer program product.
Description of Related Art
For surveying a target point, numerous geodetic surveying devices have been known since antiquity. In this case, direction or angle and usually also distance from a measuring device to the target point to be surveyed are recorded and, in particular, the absolute position of the measuring device together with reference points possibly present are detected as spatial standard data.
Well-known examples of such geodetic surveying devices include theodolite, tachymeter and total station, which is also referred to as electronic tachymeter or computer tachymeter. One geodetic measuring apparatus from the prior art is described in the publication document EP 1 686 350, for example. Such devices have electrical-sensor-based angle and, if appropriate, distance measuring functions that permit direction and distance to be determined with respect to a selected target. In this case, the angle and distance variables are established in the internal reference system of the device and, if appropriate, also have to be linked to an external reference system for absolute position determination.
In many geodetic applications, points are surveyed by virtue of specifically configured target objects being positioned there. Said target objects consist usually of a plumb rod with a reflector (e.g. an all-round prism) for defining the measurement path or the measurement point. In such surveying problems, a quantity of data, instructions, speech and further information is transmitted between target object—in particular a portable data detection device on part of the target object—and central measuring device for controlling the measurement procedure and for setting or registering measurement parameters. Examples of such data include the identification of the target object (type of employed prism), inclination of the plumb rod, height of the reflector above the ground, reflector constants or measured values such as temperature or air pressure. This information or these situation-dependent parameters are required in order to enable highly precise sighting and surveying of the measurement point defined by the plumb rod with prism.
Modern total stations generally have a compact and integrated design, with coaxial distance measuring element and computer, control and storage units usually being present in a device. Depending on the configuration level of the total station, a motorization of the sighting or targeting apparatus and—when using retroreflectors (e.g. an all-round prism) as target objects—means for automated target search and tracking moreover can be integrated. As a human-machine interface, the total station can comprise an electronic display/control unit—generally a microprocessor computer unit with electronic data storage means—with a display and input means, e.g. a keyboard. Measurement data detected by electrical sensor means are fed to the display/control unit such that the position of the target point can be established, displayed optically and stored by the display/control unit. Total stations known from the prior art can furthermore comprise a radio data interface for establishing a radio connection to external peripheral components such as e.g. a portable data detection device, which, in particular, can be embodied as a data logger or a field computer.
For sighting or targeting the target point to be surveyed, generic geodetic surveying devices have a telescopic sight, such as e.g. an optical telescope, as sighting apparatus. In general, the telescopic sight can be rotated about a vertical axis and about a horizontal tilt axis relative to a base of the measuring device, such that the telescope can be aligned on the point to be surveyed by pivoting and tilting.
The optical system or the optical visual channel of the sighting apparatus usually contains an objective lens group, an image erection system, a focusing optical system and a cross-lines grid for producing a reticle and an eyepiece, which, for example, are arranged from the object side in this sequence. The position of the focusing lens group is set dependent on the object distance in such a way that an in-focus object image is produced on the cross-lines grid arranged in the focusing plane. This object image can then be observed through the eyepiece or detected by means of e.g. a coaxially arranged camera.
The structure of generic telescopic sights of geodetic devices is shown in EP 1 081 459 or EP 1 662 278 in an exemplary manner.
Since target objects (e.g. the plumb rods with target marker such as an all-round prism usually employed for geodetic purposes) cannot be sighted precisely enough (i.e. not satisfying the geodetic accuracy requirements) with the naked eye using the sighting apparatus, despite the often provided 30-times optical magnification, conventional surveying devices in the meantime have an automatic target tracking function for prisms serving as target reflector (ATR: “automatic target recognition”) as a standard. For this, it is conventional for a further separate ATR light source—e.g. a multimode fiber output, which emits optical radiation with a wavelength in the region of 850 nm—and a specific ATR detector (e.g. CCD area sensor) sensitive to this wavelength to be additionally integrated into the telescope. By way of example, EP 2 141 450 describes a surveying device with a function for automatic sighting of a retro-reflecting target and with an automatic target tracking functionality.
Modern devices, in addition to the optical visual channel, can have a camera, which is integrated into the telescopic sight and aligned e.g. coaxially or in parallel, for detecting an image, wherein the detected image can be depicted, in particular, as live image on the display of the display/control unit and/or on a display of the peripheral device—such as e.g. of the data logger—used for remote control. In this case, the optical system of the sighting apparatus can have manual focus—e.g. an adjustment screw for changing the position of a focusing optical system—or an autofocus, wherein the focus position is changed by e.g. servomotors. By way of example, such a sighting apparatus of a geodetic surveying device is described in EP 2 219 011. Automatic focusing apparatuses for telescopic sights of geodetic devices are known from e.g. DE 197 107 22, DE 199 267 06 or DE 199 495 80.
By means of such an image detection unit, it is also possible to detect images of a measurement scene in addition to surveying specified target points. Hence, an object to be surveyed can be detected in the image and, optionally, displayed to a user on a display of the surveying device. Further information for the object can be derived on the basis of this image.
By means of appropriate image processing, it is possible, for example, to determine a surface condition for the object or a spatial extent of the object, at least in an approximate manner. Here, the spatial extent or the form of the object can be determined by means of edge extraction on the basis of the image.
For a more accurate determination of these object properties, it is possible to take account of position information for one or more points lying on the object in addition to the image information. To this end, the one point or the plurality of points are sighted and surveyed by the surveying device in an accurate fashion.
The points determined thus in terms of their position, as so-called support points, are processed together with the image information, as a result of which a more accurate statement can be made, for example about the position of the object part detected in the image.
A disadvantage in this case is that a large area topographic and geodetically accurate object survey cannot be made using a total station or means a disproportionately high time expenditure (compared to image detection of the object) since every point to be surveyed would have to be sighted individually and the position thereof would have to be determined in the case of a fixed alignment of the measurement radiation.
Moreover, determining the position of the object part imaged by the image can, in particular, only be undertaken depending on the determined support points and a high accuracy can only be achieved using a correspondingly large number of support points, wherein, furthermore, the form of the object part can likewise only be established with a very limited accuracy on the basis of image processing only (e.g. if the object has a curved surface).
At least one embodiment of the invention to provides an improved surveying device and a corresponding method, which enable improved, faster and more accurate large area object surveying of an object, in particular wherein the position of the object to be surveyed can be determined (in a geo-referenced fashion).
At least one embodiment provides for a corresponding surveying device, in particular a total station, wherein a more accurate object detection and, moreover, a provision of device-independent object coordinates for the object can be carried out.
At least one embodiment provides for a surveying device, by means of which measurement progress in respect of an absolute coordinate system (as an alternative to the internal reference system of the measuring device) can be monitored.